Implants and methods for inter-transverse process dynamic stabilization of a spinal motion segment

ABSTRACT

An implant assembly for stabilizing a spinal motion segment includes a flexible spacer member positionable between adjacent transverse processes.

BACKGROUND

Implants can be positioned between adjacent spinous processes to provideresistance to vertebral movement as a result of extension of the spinalcolumn. These implants can provide a shock absorber or bumper thatdynamically limits spinal extension. The implants can be secured to theadjacent spinous processes with looped cables or straps that extendcompletely about the spinous processes and implant to maintainpositioning of the implant between the spinous processes while alsolimiting spinal flexion. While spinous process implants provide dynamicstabilization along the spinal midline, dynamic stabilization atuni-lateral or bi-lateral locations of the posterior vertebral elementsis not achieved with such implants.

SUMMARY

There is provided spinal implants, implant assemblies and implants thatprovide uni-lateral or bi-lateral dynamic stabilization of a spinalmotion segment through the posterior vertebral elements.

According to one aspect, a spinal implant includes a spacer memberextending between opposite upper and lower ends. The upper and lowerends each include a pair of arms and a recessed surface between the pairof arms. The arms are structured to receive a respective adjacent one ofupper and lower transverse processes of a spinal motion segment. Thespacer member includes a compressible body sized and shaped to extendbetween the upper and lower transverse processes to dynamically limitmovement of the upper and lower transverse processes toward one anotherupon extension of the spinal motion segment.

According to another aspect, a spinal implant system includes a firstspacer member extending between opposite upper and lower ends structuredto receive a respective adjacent one of upper and lower transverseprocesses of a spinal motion segment at a first side of the spinalmidline. The system further includes a second spacer member extendingbetween opposite upper and lower ends structured to receive a respectiveadjacent one of upper and lower transverse processes of a spinal motionsegment at a second side of the spinal midline. Each of the spacermembers includes a compressible body sized and shaped to extend betweenthe upper and lower transverse processes to dynamically limit movementof the upper and lower transverse processes toward one another uponextension of the spinal motion segment.

According to a further aspect, a method for stabilizing a spinal motionsegment comprises: positioning a spacer member between adjacent upperand lower transverse processes of the spinal motion segment, the spacermember including an upper end contacting an inferior surface of theupper transverse process and a lower end contacting a superior surfaceof the lower transverse process; and dynamically stabilizing the spinalmotion segment with the spacer member resiliently compressing betweenthe transverse processes in response to extension of the spinal motionsegment.

These and other aspects will be discussed further below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of a posterior portion of a spinal columnmotion segment with implant assemblies engaged thereto.

FIG. 2 is a lateral view of the spinal column motion segment of FIG. 1.

FIG. 3 is an elevation view of another embodiment implant assembly.

FIG. 4 is an elevation view of another embodiment implant assembly.

FIG. 5 is an elevation view of another embodiment implant assembly.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any such alterations and furthermodifications in the illustrated devices, and such further applicationsof the principles of the invention as illustrated herein arecontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Implants are positionable between adjacent transverse processes of aspinal motion segment to dynamically stabilize and limit spinalextension and/or flexion. The implant includes a spacer member receivedbetween the transverse processes that is compressible to allow extensionmotion of the motion segment while maintaining a distraction forcebetween the transverse processes.

In one implant system, spacer members are positioned bi-laterallyrelative to a spinal motion segment in order to provide bi-lateralstabilization. In another implant system, uni-lateral stabilization isprovided by the implant system. In still other systems, multi-levelvertebral stabilization is contemplated for either uni-lateral orbi-lateral systems. The implant systems may be employed either alone orin combination with other implants, such as rods, plates, tethers,interbody fusion devices, interbody spacers, artificial discs, annulusrepair system, or staples, for example.

In a further form, one or more engaging members in the form of a tethercouples the implant to one or more posterior vertebral elements orimplants. The engaging members can be engaged to the spacer member, orextend through the spacer member. The engaging members can be engaged tothe posterior elements in a configuration that limits spinal flexion.Alternatively or additionally, the engaging members can be engaged tothe posterior elements in a manner that prevents the spacer member frombeing displaced from its implantation location between the transverseprocesses.

In FIG. 1 there is shown a spinal column segment 10 including an uppervertebra 11, a lower vertebra 15 and a spinal disc 13 therebetween alonga central axis 21 of the spinal column. The vertebrae 11, 15 and disc 13comprise a spinal motion segment, it being understood that a spinalmotion segment may include multiple vertebral levels. Upper vertebra 11includes a first upper transverse process 12 and a second uppertransverse process 16. Lower vertebra 15 includes a first lowertransverse process 14 and a second lower transverse process 18. Thetransverse processes 12, 14, 16, 18 comprise posterior elements of thevertebrae of the spinal motion segment along with the spinous processes17, 19, facets, pedicles and other posterior structures of eachvertebrae 11, 15.

A spinal implant 30 is positioned in engagement with the posteriorvertebral elements to provide dynamic spinal stabilization. Spinalimplant 30 includes a spacer member 32 extending between and contactingadjacent surfaces of transverse processes 12, 14 to limit movement ofthe spinous processes toward one another as a result of extension of thespinal motion segment. For example, spacer member 32 can include anupper end 34 in contact with inferior surface 22 of transverse process12, and a lower end 36 in contact with superior surface 26 of transverseprocess 14. Spacer member 32 can include a body structured toresiliently compress in response to extension of the spinal extension,providing resistance to the extension forces and limiting movement ofthe transverse processes 12, 14 toward one another as spacer member 32is compressed.

FIG. 1 further shows a second spinal implant 30 on the other side ofcentral axis 21 of the spinal column. The second spacer member 32 can bestructured like the other implant 30, and is configured to extendbetween and contact adjacent surfaces of transverse processes 16, 18 tolimit movement of the spinous processes toward one another as a resultof extension of the spinal motion segment. The implants 30 workbi-laterally to provide bi-lateral stabilization of spinal columnsegment 10. Additional implants 30 may be provided at one or moreadditional vertebral levels for multi-level stabilization procedures. Itis further contemplated that implants 30 may be employed touni-laterally stabilize one or more vertebral levels. The spinalimplants, either alone or in combination, can fluction to distract thespinal space and/or the spinal foramen to relieve nerve root pressure,decompress spinal elements. The implants provide overall stability whilemaintaining motion capabilities of the spinal motion segment.

As further shown in FIG. 2, spacer member 32 includes a pair of upperarms 42 and a pair of lower arms 44. Upper arms 42 define a concavelycurved upper surface 35 therebetween, and lower arms 44 define aconcavely curved lower surface 37 therebetween. The concavely curvedsurfaces 35, 37 can conform generally to or be conformable to thesurface of the transverse process against the surface is positioned.Arms 42, 44 extend along opposite sides of and receiver the respectivetransverse process 12, 14 to resist dislodgement of spacer member 32from its positioning between transverse processes 12, 14.

In its implanted orientation, spacer member 32 includes an anteriorlyoriented surface 46 and a posteriorly oriented surface 48. Anteriorlyoriented surface 46 can include a concave curvature to fit over theexiting nerve root 28 and prevent or avoid any impingement thereof.Posteriorly oriented surface 48 can be convexly curved as illustrated,or can include a concave curvature, or it can be linear in form.

In addition, each of the arm pairs 42, 44 includes a posterior arm 42 a,44 a and an anterior arm 42 b, 44 b. In the illustrated embodiment,posterior arms 42 a, 44 a have a thickness that is less than thethickness of the anterior arms 42 b, 44 b. The reduced thickness limitsthe amount of spacer material in the area where nerve root 28 exits thespinal foramen, increasing the space available for nerve root 28 topass.

In a further embodiment, it is contemplated that stiffening members canbe provided to enhance or increase the stiffness of spacer member 32.For example, as shown in FIG. 3, a stiffening member 50 is shown in theform of a band that extends about and contacts the perimeter of spacermember 32 in a direction transverse to central axis 33. Multiplestiffening members 50 can be provided about spacer member 32 to allowthe stiffness profile of spacer member 32 to be increased or decreasedby adding or removing stiffening members 50. In another embodiment,stiffening member 50 includes a width that extends along a substantialportion of the length of spacer member 32.

In FIG. 3 there is shown one embodiment shape for spacer member 32 inthe medial-lateral direction when in its implantation orientation. FIG.4 shows one embodiment of spacer member 32 positionable along the lefthand side of the spinal column and in an elevation view looking theposterior to anterior direction. Spacer member 32 extends between upperend 34 and lower end 36, and arms 42 are provided at upper end 34 andarms 44 are provided at lower end 36 as discussed above. A central axis33 divides spacer member 32 into a right hand or medial side and a lefthand or lateral side. Spacer member 32 includes a medial surface 52extending along the medial side and a lateral surface 54 extending alongthe lateral side. Adjacent lower end 36, medial surface 52 is offsetlaterally toward or to one side of central axis 33 along lower arms 44.Medial surface 52 extends transversely to central axis 33 from lowerarms 44 to upper arms 42 at upper end 34. Along upper arms 42, medialsurface 52 is offset medially of central axis 33 and also offsetmedially with respect to the portion of medial surface 52 along lowerarms 44.

The offsetting medial surface 52 is shaped to facilitate placement ofspacer member 32 along or against the bony structure and shapes at thejunctions of the transverse process and pedicle. By allowing placementof spacer member 32 as close as possible to the junction of thetransverse process with the pedicle, the moment arm on the transverseprocess is minimized. In another embodiment, spacer member 32 is madewith material properties that deform to allow conformance upon contactof spacer member 32 with the bony structure. In still other embodiments,the medial and lateral surfaces can be parallel to one another.

Referring now to FIG. 5, there is shown an implant assembly 130. Implantassembly 130 includes a spacer member 132 having a body extendingbetween an upper end 134 and a lower end 136. A first pair of arms 142are provided adjacent upper end 134, and a second pair of arms 144 areprovided adjacent lower end 136. Spacer member 132 is similar to spacermember 32 discussed above and is structured for positioning between andreceiving adjacent upper and lower transverse processes of a spinalmotion segment. However, implant assembly 130 include an engaging member150 extending therefrom to attach spacer member 132 to posteriorvertebral elements or implants of the spinal motion segment.

Spacer member 132 includes through-passages 148 extending betweenopposite sides thereof, which include the anterior and posterior sidesof spacer member 132 in the illustrated embodiment. Passages 148 receiveengaging member 150 therethrough. Engaging member 150 may comprisemultiple engaging members, or a single engaging member looped throughpassages 148. Still other embodiments contemplate a single passage 148,or three or more passages 148, through which one or more engagingmembers 150 are positioned.

Engaging member 150 can be in the form of a tether, cord, wire, cable,suture, band, strap, belt, or other suitable structure for manipulationand securement to one or more posterior vertebral elements. Engagingmember 150 may be wrapped or positioned around posterior vertebralelements and then maintained in position with a crimp or other suitablefastener. Furthermore, engaging member 150 can be coupled to spacermember 132 in any suitable manner. In one embodiment, engaging member150 is movably coupled to spacer member 132. Engaging member 150 can beintegrally formed with spacer member 132, or can be attached by afastener, suture, anchor, cable, link, over-molding or other suitableconnection. Spacer member 132 can be provided with ears, eyelets,recesses or other suitable structure to facilitate engagement ofengaging member 150 to spacer member 132. Engaging member 150 may beemployed in spinal stabilization procedures where it is desired to limitspinal flexion by, for example, wrapping engaging member 150 about thesuperior surface of the upper transverse process and the inferiorsurface of the lower transverse process. Engaging member mayalternatively be employed as a retention mechanism to maintain spacermember 132 in position between the transverse processes.

With respect to the various embodiments described herein, the engagingmember can be joined or fixed to the spacer member using various devicesand/or techniques, or can be integrally formed with or form an extensionof the spacer member. The spacer member can be joined or attached to theengaging member by, for example, sewing the engaging member to thespacer member, thermal welding or bonding, adhesive bonding, threedimensional weaving or braiding, screws, staples, pins, tacks or rivetfixation. Furthermore, the engaging member can be secured to the spacermember either before or after the spacing member is placed between thetransverse processes. The engaging member can be engaged to otherengaging members of other implant assemblies or to other implantsengaged to the spinal column in the surgical procedure.

The spacer member can be fabricated from components that are flexible orexhibit at least some flexibility. Examples of such components includewoven fabric tubing, woven and non-woven mesh, or braided or wovenstructures, sutures, tethers, cords, planar members, bands, wires,cables, or any other component capable of extending between andsupporting the adjacent spinous processes. Additionally, the spacermember may be resilient and/or elastic so it can assume various shapesduring and after insertion and attachment.

The spacer member can be made from any biocompatible material, materialof synthetic or natural origin, and material of a resorbable ornon-resorbable nature. Suitable examples of spacer member materialinclude autograft, allograft or xenograft; tissue materials includingsoft tissues, connective tissues, demineralized bone matrix andcombinations thereof; resorbable materials including polylactide,polyglycolide, tyrosine-derived polycarbonate, polyanhydride,polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite,bioactive glass, collagen, albumin, fibrinogen and combinations thereof;and non-resorbable materials including polyethylene, polyester,polyvinyl alcohol, polyacrylonitrile, polyamide, polytetrafluorethylene,poly-paraphenylene terephthalamide, polyetheretherketone, cellulose, andcombinations thereof.

The engaging members described herein can be made from any one orcombinations of biocompatible material, including synthetic or naturalautograft, allograft or xenograft tissues, and can be resorbable ornon-resorbable nature. Examples of tissue materials include hardtissues, connective tissues, demineralized bone matrix and combinationsthereof. Further examples of resorbable materials are polylactide,polyglycolide, tyrosine-derived polycarbonate, polyanhydride,polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite,bioactive glass, and combinations thereof. Further examples ofnon-resorbable materials are carbon-reinforced polymer composites,shape-memory alloys, titanium, titanium alloys, cobalt chrome alloys,stainless steel, and combinations thereof.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

1. A spinal implant, comprising: a spacer member extending betweenopposite upper and lower ends, said upper and lower ends each includinga pair of arms and a recessed surface between said pair of arms, saidarms being structured to receive a respective adjacent one of upper andlower transverse processes of a spinal motion segment, said spacermember including a compressible body sized and shaped to extend betweenthe upper and lower transverse processes to dynamically limit movementof the upper and lower transverse processes toward one another uponextension of the spinal motion segment.
 2. The implant of claim 1,wherein said body includes a posterior surface and an anterior surfacein an implantation orientation between the upper and lower transverseprocesses, said anterior and posterior surfaces extending between saidfirst and second ends, wherein said anterior surface includes a concavecurvature between said first and second ends.
 3. The implant of claim 2,wherein said posterior surface is convexly curved between said first andsecond ends.
 4. The implant of claim 1, further comprising at least oneband extending about said body in contact therewith about a perimeter ofsaid body, said at least one band compressing said body about saidperimeter.
 5. The implant of claim 1, wherein each of said arm pairsincludes a posterior arm positionable along a posterior side of thetransverse process and an anterior arm positionable along an anteriorside of the transverse process.
 6. The implant of claim 5, wherein inthe implantation orientation said posterior arms each include athickness in the anterior-posterior direction that is greater than athickness of each of said anterior arms in the anterior-posteriordirection.
 7. The implant of claim 5, wherein said body extends along acentral axis between said first and second ends, said arms at said upperend of said spacer member being offset in the medial direction from saidarms at said lower end of said spacer member.
 8. The implant of claim 1,further comprising at least one tether engaged to said body andextending therefrom, said tether being positionable about posteriorelements of the spinal motion segment.
 9. The implant of claim 8,wherein said body includes at least one bore extending therethroughbetween a posteriorly oriented side and an anteriorly oriented side ofsaid body when positioned between the upper and lower transverseprocesses, said at least one tether extending through said at least onebore.
 10. The implant of claim 9, further comprising a second borethrough said body adjacent to and paralleling said first bore.
 11. Aspinal implant system, comprising: a first spacer member extendingbetween opposite upper and lower ends structured to receive a respectiveadjacent one of upper and lower transverse processes of a spinal motionsegment at a first side of the spinal midline; and a second spacermember extending between opposite upper and lower ends structured toreceive a respective adjacent one of upper and lower transverseprocesses of a spinal motion segment at a second side of the spinalmidline, wherein each of said spacer members includes a compressiblebody sized and shaped to extend between the upper and lower transverseprocesses to dynamically limit movement of the upper and lowertransverse processes toward one another upon extension of the spinalmotion segment.
 12. The system of claim 11, further comprising anengaging member for each of said spacer members, each of said engagingmembers being in the form of a tether positionable about posteriorelements of the spinal motion segment to secure said spacer memberthereto.
 13. The system of claim 1 1, wherein said body of each of saidspacer members includes a posterior surface and an anterior surface inan implantation orientation between the upper and lower transverseprocesses, said anterior and posterior surfaces extending between saidfirst and second ends, wherein said anterior surface includes a concavecurvature between said first and second ends.
 14. The system of claim13, wherein for each of said spacer members said posterior surface isconvexly curved between said first and second ends.
 15. The system ofclaim 1, wherein for each of said spacer members said body includes apair of upper arms defining a recessed surface therebetween forreceiving the upper transverse process and a pair of lower arms defininga recessed surface therebetween for receiving the lower transverseprocess.
 16. The system of claim 15, wherein each of said pair of armsincludes a posterior arm positionable along a posterior side of thetransverse process and an anterior arm positionable along an anteriorside of the transverse process.
 17. The system of claim 16, wherein inthe implantation orientation of each of said spacer members saidposterior arms each include a thickness in the anterior-posteriordirection that is greater than a thickness of each of said anterior armsin the anterior-posterior direction.
 18. A method for stabilizing aspinal motion segment, comprising: positioning a spacer member betweenadjacent upper and lower transverse processes of the spinal motionsegment, the spacer member including an upper end contacting an inferiorsurface of the upper transverse process and a lower end contacting asuperior surface of the lower transverse process; and dynamicallystabilizing the spinal motion segment with the spacer member resilientlycompressing between the transverse processes in response to extension ofthe spinal motion segment.
 19. The method of claim 18, furthercomprising positioning each of the upper and lower transverse processesbetween arms at each of the upper and lower ends of the spacer member.20. The method of claim 18, further comprising engaging the spacermember to posterior vertebral elements of the spinal motion segment witha tether.
 21. The method of claim 18, further comprising increasing astiffness of the spacer member with a stiffening member extending aboutthe body of the spacer member transversely to a central axis of thebody.
 22. The method of claim 18, further comprising maintainingclearance of a spinal foramen by concavely curving an anterior surfaceof the spacer member.
 23. The method of claim 21, further comprisingpositioning a second spacer member between second adjacent upper andlower transverse processes of the spinal motion segment on a side of thespinal motion segment opposite the other spacer member, the secondspacer member including an upper end contacting an inferior surface ofthe second upper transverse process and a lower end contacting asuperior surface of the second lower transverse process; and dynamicallystabilizing the spinal motion segment with the second spacer memberresiliently compressing between the second transverse processes inresponse to extension of the spinal motion segment.